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Date: Mon, 24 Oct 2022 11:19:31 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Kees Cook <keescook@...omium.org>, Dave Hansen <dave.hansen@...el.com>, Sean Christopherson <seanjc@...gle.com> Subject: Re: [PATCH] x86/mm: Do not verify W^X at boot up On Mon, Oct 24, 2022 at 8:45 AM Steven Rostedt <rostedt@...dmis.org> wrote: > > From: "Steven Rostedt (Google)" <rostedt@...dmis.org> > > Adding on the kernel command line "ftrace=function" triggered: > > CPA detected W^X violation: 8000000000000063 -> 0000000000000063 range: Hmm. The cause of this actually seems to be this if (likely(system_state != SYSTEM_BOOTING)) set_memory_ro((unsigned long)trampoline, npages); set_memory_x((unsigned long)trampoline, npages); return (unsigned long)trampoline; in create_trampoline(). And that in turn is because of commit 59566b0b622e ("x86/ftrace: Have ftrace trampolines turn read-only at the end of system boot up"), which in turn is because of if (unlikely(system_state == SYSTEM_BOOTING)) { text_poke_early(addr, opcode, len); return; } in text_poke_bp(). And that, in turn, is because PeterZ ended up special-casing this all in commit 768ae4406a5c ("x86/ftrace: Use text_poke()") Maybe we should just strive to get rid of all these SYSTEM_BOOTING special cases, instead of adding yet another a new one. There's presumably "it slows down boot" reason to avoid the full text_poke_bp() dance, but do we really care for the "ftrace=function" case? Linus
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